This invention relates to the drilling of wells for the production of geothermal steam and more particularly to a method for reducing the hydrogen sulfide content of geothermal steam released during the drilling operation so as to abate the emission of hydrogen sulfide to the environment.
In recent years the harnessing of geothermal energy has become of increasing concern and interest. Typically the geothermal thermal energy is obtained by recovering steam, hot water or hot aqueous brines from underground reservoirs and utilizing the energy values of these hot fluids either directly or indirectly to drive turbines and the like. The hot fluids are normally recovered from the underground reservoir by drilling a well of sufficient depth to penetrate the fluid-bearing portion of the reservoir. During such drilling operations conventional drilling fluids are utilized for removing the cuttings from the well bore. Typically air is utilized as the drilling fluid when the well bore has reached the hot fluid-bearing portion of the reservoir and the returning air, in addition to containing formation cuttings, also contains a substantial amount of steam which escapes from the reservoir during the drilling operation. The returning air and steam is normally led from the well to a separator where the particulate matter is separated from the stream of air and steam and thence the air and steam are discharged to the atmosphere,
Geothermal steam typically contains hydrogen sulfide gas which is discharged along with the steam. Consequently the emission of untreated geothermal steam to the atmosphere is undesirable both from the standpoint of health and safety and from the standpoint of the odor of the hydrogen sulfide. However, during the well drilling operation itself, the geothermal steam escaping from the reservoir is conventionally emitted directly to the atmosphere without treatment to remove hydrogen sulfide.
Processes are known in the prior art for the treatment of gas streams to absorb hydrogen sulfide therefrom. For example, it is known that contacting a hydrogen sulfide containing gas stream with an alkaline hydrogen peroxide solution will remove hydrogen sulfide from a gas stream. However, these processes involve the use of packed columns or other gas liquid contact devices which are totally impractical and unsuited for use in well drilling operations of the type described. In addition these processes are not concerned with the treatment of hot fluids having the air-liquid volume ratio of geothermal steam produced during drilling operations.
Accordingly it is an object of the present invention to provide a method for the abatement of hydrogen sulfide discharge into the atmosphere during well drilling operations.
It is another object of the present invention to provide a method for reducing the hydrogen sulfide content of geothermally produced steam by a process which is readily adaptable for use in conventional well drilling operations and which does not substantially hamper or interfere with the well drilling operations.
These and other objects and advantages of the present invention will be apparent from the following detailed description and drawings.